Handler

package com.example.i310_54.myapplication08;

import android.graphics.Color;
import android.os.CountDownTimer;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.ProgressBar;

import java.util.Random;

public class MainActivity extends AppCompatActivity {

    String TAG="EUNBI";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    Handler handler=new Handler(){
        @Override
        public void handleMessage(Message msg) {

            switch (msg.what){
                
                case 100:
                    Log.d(TAG, "handleMessage: 100"); 
                    handler.sendEmptyMessageDelayed(100,500);
                    break;
                case 200:
                    Log.d(TAG, "handleMessage: 200");
                    handler.sendEmptyMessageDelayed(200,700);
                    break; 
            }
          
        }
    };
    public void f1(View view) {

        handler.sendEmptyMessage(100);
    }

    public void f2(View view) {
        handler.sendEmptyMessage(200);
    }

    public void f3(View view) {
        handler.removeMessages(100);
    }

    public void f4(View view) {
        handler.removeMessages(200);
    }
}